Human Tau is encoded by the microtubule-associated protein Tau gene, MAPT, located on chromosome 17q21. The adult human brain contains six main Tau isoforms which are generated by alternative splicing of exon 2 (E2), E3, and E10. These isoforms differ depending on the number of 29-residue repeat regions near the N-terminus. Tau isoforms containing 0, 1, or 2 inserts are known as 0N, 1N, and 2N, respectively. Unprocessed Tau isoforms also contain either 3 (“3R”) or 4 (“4R”) microtubule-binding repeat domains. The second of these repeat domains is encoded by E10 and is not included in 3R Tau isoforms (FIG. 1).
Although Tau is usually highly soluble, under pathological conditions, it can aggregate into paired helical filaments, neurofibrillary tangles and other structures that define a large spectrum of neurodegenerative diseases termed Tauopathies. Tauopathy thus refers to a class of neurodegenerative diseases associated with aggregation of the microtubule-associated protein Tau, including Alzheimer's disease (AD), progressive supranuclear palsy (PSP), and frontotemporal dementia (FTD).
The underlying mechanism of Tau-mediated neurotoxicity is poorly understood and the trigger for Tau aggregation in neurons is yet to be elucidated. Thus, while therapeutic approaches targeting Tau are being explored, there remains a need for specific and effective therapeutic agents that target Tau.